With the development and progress of science and technology, users are imposing stricter requirements on input methods employed by their cell phones and tablet computers. They have been unsatisfied with the traditional keyboard-based input modes, and are gradually turning to the more convenient touch-based ones. The existing commercially available touch input devices are mostly resistive and capacitive products. With their advantages in higher sensitivity, and since it is easier for them to provide multi-touch functions, capacitive touch screens are gradually replacing their resistive touch screen counterparts and predominating the market. There are two kinds of capacitive touch screens, the surface capacitive type and projected capacitive type, and the projected capacitive type can be further categorized into mutual-capacitive and self-capacitive types. A touch screen of the mutual-capacitive type includes two arrays of electrodes, arranged orthogonal to each other, and a touch screen controller. One of the electrode arrays serves as actuation electrodes, and the other as detection electrodes. The electrodes form mutual capacitances with those of the other array or form self-capacitances with a ground. Under the effect of an actuation module, the actuation electrodes produce touch-screen actuation signals, which are received by the detection electrodes. Upon a grounded conductive object (e.g., a finger) approaching the capacitive touch screen, the mutual capacitances between the actuation and detection electrodes will vary, and by detecting the mutual capacitance variations, the detection electrodes are capable of determining the location of the touch point. In contrast, a self-capacitive touch screen has electrodes functioning as both actuation and detection electrodes. The touch screen controller actuates one of the electrodes and determines whether there is a grounded conductive object in its vicinity by detecting a change in the capacitance of the one of the electrodes. A surface capacitive touch screen has four electrodes projecting from its respective corners and works basically in a similar way as above, i.e., detecting the location of a touch point from capacitance variations caused by the approaching of a conductive object.
Depending on whether they are electrically powered, touch screen styluses are grouped into passive and active ones. A passive stylus simply mimics a human finger by means of a conductive object (e.g., a conductor or conductive rubber, etc.) which forms a capacitance between its tip and conductive touch screen actuation, thus altering the detection results of the touch screen. Such a passive styluses is, however, disadvantageous in having a relative bulky tip (usually greater than 2 mm).
Active capacitive styluses include a signal processing module disposed therein for actively detecting a touch-screen actuation signal, as well as a conductive tip which can be made as thin as an oscilloscope probe and is capable of coupling a signal into the signal processing module in the active capacitive stylus for further processing and outputting. Active capacitive styluses can also be divided into two groups, Electro-Magnetic Resonance (EMR) and active capacitive styluses. In order to enable an EMR stylus to provide writing functions, the touch screen is required to have additional hardware such as an EMR screen layer or a sensor layer. This additional hardware not only leads to increases in thickness, cost and industrial design inferiority, but also makes the stylus unable to be used with the existing commercially available products that are equipped with only traditional touch screens. On the contrary, active capacitive styluses do not need the EMR screen layer or the sensor layer that increases screen thickness and can be directly used with the existing commercially available touch screens.
U.S. Pub. Nos. US20120154340 and US20130002606 each disclose an active capacitive stylus designed to have separate detection and actuation electrodes. These styluses are, however, associated with shortcomings described as follows:
One of the shortcomings is that both the active capacitive styluses disclosed respectively in U.S. Pub. Nos. US20120154340 and US20130002606 are configured to generate a feedback actuation signal from a bulky stylus tip or a stylus body that is spaced apart from the touch screen by a rather distance, which will make the feedback actuation signal, in case of a human user holding the stylus body in a titled orientation with respect to the touch screen just in the same way as most persons customarily do when writing with a stylus, have an intensity distribution on the touch screen that is not centered at the tip but is concentrated on the side of the screen nearer to the stylus body. This deviation is unable to be corrected by a subsequent algorithm because the touch screen controller or the host has no idea of the tilt slope of the stylus body of the active capacitive stylus.
Another shortcoming is that in the design of the U.S. Pub. Nos. US20120154340 and US20130002606 in which the detection and actuation electrodes are separated from each other and the detection and feedback actuation are carried out in a synchronous manner. So, if an inadequate isolation is provided between the electrodes, a generated actuation signal will be coupled into the detection electrodes and cause oscillation.